An overlock sewing machine is provided with a plurality of loopers, and since it is necessary to thread each of the loopers with respectively different looper threads, threading operations were troublesome.
Patent Document 1 discloses a device for threading a thread to a hollow looper point using compressed air.
Patent Document 2 discloses a compressed air path switching device corresponding to a plurality of loopers.
These techniques have enabled easy threading operations of looper threads to loopers.
On the one hand, the devices disclosed in Patent Document 1 and Patent Document 2 mainly included the following two issues.
The first issue is that when a threading enabled phase is detected and the phase is to be maintained, operations of pressing a fixing button and operations of rotating a thread take-up lever need to be performed simultaneously so that operations need to be made using both hands.
The second issue is that it can be hardly determined at a glance whether the overlock sewing machine is in a “sewing enabled state” or in a “threading state (or threading preparing state)”.
In the device disclosed in Patent Document 3, there are provided a push button including a control pin and a control groove cam portion receiving the control pin, wherein the push button, the control groove cam portion and a main shaft are separately operable with one hand.